A lithium-ion secondary battery in which a negative electrode is formed by using a material capable of absorbing and discharging lithium ions is capable of restraining deposit of dendrite to a higher extent than a lithium battery in which the negative electrode is formed by using metallic lithium. Therefore the former battery has an advantage of capable of preventing the occurrence of a short circuit and has enhanced safety.
In recent years, the lithium secondary battery is demanded to have a high capacity and is charged and discharged at high current to use it for equipment which is operated at a high power. Thereby metal lithium may deposit on the negative electrode, and an internal short circuit may occur. In the worst case, there is a fear that heat is generated and an ignition accident occurs.
Owing to a demanded high capacity of a positive electrode material containing a lithium metal oxide or a negative electrode material containing a carbon-based material, devices are conventionally proposed to allow absorbing and discharging reactions to be sufficiently accomplished at the negative electrode to prevent metal lithium from depositing on the negative electrode. In addition devices are proposed to increase specific surface areas of electrodes by decreasing the diameters of particles of an active substance. Further the electrodes are so designed as to increase the areas thereof. Although these devices progresses the designing of the electrode in a safe direction, measures against the occurrence of a short circuit caused by the drop and peeling of the active substance in the production of a battery are insufficient. Therefore devices for improving the power collection foil are proposed. For example, the following power collection materials are known: the power collection material which is reticulate, consists of the hole-formed punching metal or has lath processing performed thereon (patent document 1), the power collection material having the metal foil having irregularities formed on its surface (patent document 2), and the power collection foil which has a plurality of holes penetrating therethrough, in which the peripheries of the holes project from at least one surface of the foil-like power collection material, and the thickness of the foil-like power collection material including the projected part formed on the periphery of the hole is more than 3% and not more than 25% of the total thickness of one polar plate which is the sum of the thickness of the mixed agent layer and that of the power collection material of the negative electrode or the positive electrode (patent document 3).
But the above-described proposed power collection foil which is reticulate, consists of the hole-formed punching metal or has lath processing performed thereon has a lower strength than that which the normal electrode power collection material should have. The method of forming the irregularities on the foil is not different from a contact method for an ordinary flat foil used as a technique for preventing the peeling of an active substance. Therefore when a battery is repeatingly charged and discharged at high current, the active substance of the positive and that of the negative electrodes expand and contract and peel and drop from the power collection foil. Thereby a short circuit is induced, which may result in the generation of heat. In addition these methods cause metal powder of the power collection foil generated in processing it to slip into the battery, thus causing a problem of the occurrence of the short circuit.
As a production method for producing electrodes for the lithium secondary battery, there is disclosed the apparatus for successively producing the paste type electrode plates while the apparatus is successively measuring the weight of paste without contact between the apparatus and paste (patent document 4).
There is disclosed the production method for producing the electrode for the lithium secondary battery having the first step of forming the active substance film which absorbs and discharges lithium on the power collection foil by using a vacuum process and the second step of removing the projections formed on the surface of the film of the active substance by the blade having the straight edge. In the second step, the projections are removed by moving the film of the active substance with the straight edge of the blade being spaced at the predetermined interval from the surface of the active substance film (patent document 5).
But the apparatus has a problem that in winding the power collection foil in a roll shape through which a plurality of the holes penetrating the power collection foil is formed, metal powder generated while the foil is being processed remains on the surface thereof and slips into the mixed agent layer in forming the mixed agent layer on the power collection foil thereafter.